Ethylene glycol is a chemical which has found wide use in industry. It is used, for example, in the preparation of plasticizers for vinyl polymers and as a component in polyester fibers and antifreeze formulations. In view of its many uses, there is a need to find new and more economical methods for preparing the ethylene glycol.
Proposed methods of making ethylene glycol involve the reaction of carbon monoxide with hydrogen in the presence of variously proposed catalyst systems. In general, the mixture of carbon monoxide and hydrogen, commonly known as synthesis gas, is reacted at elevated temperatures and pressures in the presence of the proposed catalysts. For example, Belgium Pat. No. 793,086 and U.S. Pat. No. 3,940,432, describe the cosynthesis of ethylene glycol and methanol from mixtures of carbon monoxide and hydrogen using a complex rhodium catalyst. U.S. Pat. No. 3,833,634 describes the use of various other metals as catalysts but indicates that only rhodium and cobalt were effective in producing the ethylene glycol. Here the typical yield of ethylene glycol produced was 9.8 parts out of 58 parts.
U.S. Pat. No. 3,989,799 discloses a series of carbonyl mixed metal salt useful as catalyst in the reaction between carbon monoxide and hydrogen to produce oxygenated compounds. There are no selectivities reported for particular products such as ethylene glycol. There is no mention of the use of a quaternary onium salt.
In U.S. Pat. No. 4,013,700, Cawse discloses a process for producing polyhydric alcohols, their ether and ester derivatives in the presence of a quaternary phosphonium cation and a rhodium carbonyl complex. This system produces moderate quantities of ethylene glycol as demonstrated by yields of 4.2 grams and less.
U.S. Pat. No. 4,265,828, Knifton, 1981, discloses a process of making ethylene glycol which comprises the steps of contacting a mixture of CO and H.sub.2 with a catalyst system comprising a ruthenium-containing compound dispersed in a low-melting quaternary phosphonium or ammonium base or salt and heating said resultant reaction mixture under a pressure of 500 psi or greater at a temperature of at least 150.degree. C. for a sufficient time to provide said ethylene glycol. The highest yield of ethylene glycol obtained by this process was 17.6 weight percent.
In U.S. Pat. No. 4,315,994 by Knifton, alkylene glycols and their ethers are produced by contacting a mixture of carbon monoxide with a bimetallic catalyst system comprising ruthenium(III) acetylacetonate and rhodium(III) acetylacetonate dispersed in a low melting quaternary onium base or salt at a pressure of at least 150.degree. C. The highest reported selectivity for ethylene glycol was 18.5 weight percent.
Many of these processes are limited by the nature and activity of the catalyst systems. Most catalysts provide only moderate selectivity to desired glycol, limited solubility and/or are expensive to prepare.
It would be a significant advance in the art to provide an improved method for preparing ethylene glycol and monohydric alcohols which provides ethylene glycol with greater yields and selectivity.